Electrophysiological and Olfactometer Responses of Two Histerid Predators to Three Pine Bark Beetle Pheromones

We measured electrophysiological responses in the antennae of two predaceous hister beetles, Platysoma parallelum and Plegaderus transversus, exposed to racemic mixtures of primary aggregation pheromones of scolytid bark beetle prey, ipsenol, ipsdienol, and frontalin. No significant differences were found for either histerid species between male and female antennal responses to any of the three pheromones. Measurement of antennal threshold responses indicated that Pla. parallelum has increasing antennal sensitivity to ipsdienol, ipsenol, and frontalin. In contrast, Ple. transversus exhibited similar detection thresholds to all three pheromones. Pla. parallelum antennae exhibited different response amplitudes to the three pheromones at quantities above the detection threshold, while Ple. transversus had similar responses to each. Behavioral responses to the same three pheromones were evaluated for both histerid species using pedestrian olfactometer bioassays. Both species were attracted to frontalin and ipsenol, but not ipsdienol. Pla. parallelum was significantly more attracted to frontalin than ipsenol, while Ple. transversus showed no significant preference for either compound. Our results suggest that histerids that prey upon pine bark beetles may have different host or host habitat preferences, which could reduce interspecific competition.